Preparation of crystalline materials



s a-uoa AU 11? ax EWfaii'ER 9 March 1946. s. H. FOSTER ETAL 2,395,857

PREPARATION OF CRYSTALLINE MATERIALS Filed Nov. 5, 1943 260. CHEMISIRY, CARBON CQMHPUUNDS.

Patented Mar. 5, 1946 EXAiili AER UNITED STATES PATENT OFFICE PREPARATION OF CRYSTALLINE MATERIALS Application November 5, 1943, Serial No. 509,042

3 Claims.

This invention relates to a process for preparing crystalline and erystallizable substances in a very fine state of subdivision, and contemplates such improvements and refinements in the production of such substances as result in a product having certain highly desirable properties and characteristics. More particularly it embraces the production of nitroguanidine and similar substances in an extremely minute crystalline state. This is a continuation-in-part of our co-pending agglication, Ser. No. 417,064, filed October 30, l 1.

Heretofore it has been diflicult and frequently impossible to prepare such crystalline substances as, for example, nitroguanidine in the form of discrete crystals of a size less than about microns in width or less than about 300 or 400 microns in length. The usual methods of crystallization or recrystallization, even when supplemented by subsequent grinding or ball-milling in a porcelain mill ordinarily result in the production of much larger crystalline structures. Moreover. the grinding of such materials as are explosive in nature is a distinct hazard both to the workmen engaged therein and to the plants carrying out the process. In addition, however, such grinding simultaneously effects but a slight decrease in particle size.

It is an object of this invention to provide a method for the production of nitroguanidine of extremely small size in an efficient and economical manner. A further object is to prepare nitroguanidine in the form of small and uniformly very fine crystals. More specifically, it is an object of this invention to control the crystal habit, particularly the size, shape and form of crystals of nitroguanidine and to provide certain improved methods for the manufacture of nitroguanidine which facilitate the obtainment of a product having a novel and desirable crystal habit. It is also an object hereof to obtain, with the aid of a chemical modifier, crystals of nitroguanidine which are smaller and finer than those ordinarily obtained in the course of a conventional physical crystallization. A further object is to provide a method wherein, by the addition of a wetting agent or dispersing agent before the final drying step, the ultimate individual crystals are obtained in such a state as to be free from branching and aggregation and remain as separate particles when stored for prolonged periods in the dry state. Still other and further objects will become apparent upon reading the following description wherein a number of specific embodiments of the invention are given.

This invention is based principally upon the discovery that a coating or shell is formed by an included amino or similar nitrogen containing compound, on and about the minute nucleus of a precipitated crystalline substance, such as nitroguanidine, immediately upon precipitation or for mation from its solutions provided small amounts of such an amino or similar nitrogen containing compound are present in solution during the precipitation.

The best conditions for the physical crystallization of soluble materials such as nitroguanidine have heretofore been attained by preparing a saturated solution of the nitroguanidine in hot water and then suddenly cooling the solution as by spray cooling, chilling. or discharging it into an ice cold liquid or by utilizing equivalent means for cooling the nitroguanidine solution. This invention embodies the addition of a small amount of a foreign substance, such as an amino or similar nitrogen containing compound, to the hot aqueous solution of nitroguanidine before its crystallization, and precipitating the solute therefrom in the form of a pure nitroguanidine in such a fine degree of subdivision as has been impossible to obtain heretofore, by the conventional methods.

In its broadest aspects, the method herein disclosed contemplates the modification of crystal habit, particularly particle size, by the addition of any one of a number of different foreign substances to a solution of nitroguanidine before recrystallization and allowing this additive to remain in solution during the recrystallization. Such a method can be carried out in accordance with the principles of this invention by rapidly cooling a saturated solution of nitroguanidine to which has been added a small amount of a modifying compound or addition agent, e. g. 1% of a material containing an amino or a similar nitrogen containing group such as ethylene diamine, diethylene triamine, triethylene tetramine, and tetraethylene pentamine, amino acids, including glue, casein and the like. In addition to the above substances a synthetically prepared wetting agent also preferably containing an amino group, such as lauryl biguanide acetate; 1,3-diethylol, 5-butyl biguanide diacetate; monoethylol cyanamide condensed with ethylene diamine; acylated amides of polyethylene polyamines and the like, among others, may be used as the addition agent.

More particularly, it has been found that nitroguanidine crystals having a thickness of less than 5 microns and a length of less than microns can be prepared by the addition of ethylol dodecyl biguanide acetate to a nitroguanidine solution in an amount of 0.3% based on the total solution. Similar effects can be obtained by the addition of about 0.6% ethylene diamine, diethylene triamine, triethylene tetramine and tetraethylene pentamine, individually or as a mixture. In their order of effectiveness for the purposes of this invention these individual compounds may be tentatively arranged in the following sequence: diethylene triamine triethylene tetramine tetraethylene pentamine. The addition of ethylol dodecyl biguanide acetate up to about 1.0% is also effective. Optimum results are obtained when the pH of the solution is adiusted to about 8. Preferably, acetic acid can be used to attain this pH after the addition of the particular modifying agent.

In some instances the use of individual additives has been found to yield a crystalline product which may necessitate additional processing. Thus, for example, ethylene diamine may result in a product which dries to form hard lumps or of nitroguanidine crystals prepared in accordance with the method described below in Example 2.

The careful comparison, microscopical and 5 otherwise, of the products prepared in several different ways shows clearly the superiority of nitroguanidine prepared by the methods of this invention, particularly for nitroguanidine which is to be incorporated in propellent powders.

aggregates which are not readily broken up by Moreover, when prepared as herein described, a micropulverizing. However, such lumps are easmore uniform product is obtained, very little ily eliminated by washing the crystals with water variation being exhibited from the maximum to containing about 0.1% of ethanol dodecyl bithe minimum crystal size. guanide acetate or a similar wetting agent. The following examples are included herein in Although it is not desired to be limited by any order to facilitate a more complete understandtheory as to the mode of operation of the addiing of the invention. A number of variations in tives disclosed in this invention when used for the process are included below in order to illusthe formation of such discrete and small crystaltrate the extended scope of the procedure herein line precipitates, it is believed that the modifying disclosed. compound shows preferential adsorption on cer- EXAMPLE 1 tain crystallographic planes, covering portions or all of the external surface of each crystal nucleus 7 gljams of coarse crystanme mtroguamdme as formed. This adsorbed material efiectively was d1ssolved 1 aboufi 100 of Watersmall prevents further crystal growth as by accretion DQ 8 Of this solution, about 2 to 4 cc., were on the first formed crystal nucleus. Further- Wlthdrawn and {mxed m test tube wlth 1 to 3%, more, there is a possibility that the solubility of based on {ltroguamdme present of ethylol the nitroguanidine at the crystallization temperfiodecyl bleuamde acetate' T test was ature is decreased by the addition agent. This m a beaker of boning Water the increases the number of crystal nuclei formed and mtroguamfime a completely dls solved' A correspondingly decreases their size. As a result non thls m was Into a test W of the addition of the above modifying compounds 00111131111115 y The p clpltated crystalline to a hot aqueous solution of nitroguanidine of nitroguanidine was examined microscopically in about 7.5% concentration and subjecting the so- Prder 9 measure the length and cross'sectwn cf lution to a subsequent Very rapid cooling, as by its individual crystals. The resultant crystals spraying or otherwise cooling the same, crystals were predIPinant1y f very Small namely of nitroguanidine having a size of the order of 2.5 about mlcrons wlde by about 20 mlcrons long' microns in width and 20 microns in length are EXAMPLE 2 obtained. An additional advantage of the process of this invention is found in that the product An aqueous solution of nitroguanidine of about thus prepared is far more stable than a similar 40 7.5% strength was prepared and from 0.3 to 3%, product crystallized in the absence of such a preferably about 1%, of a modifying agent, such modifying compound. This may be attributed to as ethylol dodecyl biguanide acetate, was added. the addition of amines which effectively neutral- This solution was heated in an autoclave to about ize any acidity developed in the nitroguanidine 100 C. and then sprayed into water having a as a result of its decomposition during storage. temperature of 25 C. in an enclosed spray cham- This stability is due principally to the fact that her. The precipitate formed was examined mithe fine crystals of nitroguanidine contain minute croscopically and showed a decided increase in amounts of the addition agent. Depending on the proportion of nitroguanidine crystals about the addition agent used, the crystals can be ren- 2.5 microns in width by about 20 microns in length dered more or less readily dispersible in water or as compared to nitroguanidine precipitated from other media. a similar solution but which, however, was pre- The improvements and advantages of the prespared without the addition of the particular modent invention are more readily appreciated when ifying agent above. The latter crystals were considered in conjunction with the appended mlabout 5 x 150 microns in size. p oto aphs, in which: In the following examples an aqueous solution F 1 is a r pro uc ion of a photomicr eraph of nitroguanidine of 7.5% strength was prepared of nitroguanidine crystals prepared without a and, after adding the modifier indicated, the solumodifier and more particularly referred to in tion was heated to a temperature of 102 to 105 Example 3; and C. and spray cooled from a blowcase under a pres- Fig. 2 is a reproduction of a photomicrograph sure of pounds per square inch.

Particle size by number percent of tota Example Modifier Width Length s NonePhlank") 30.7 47.7 21.6 All about 151 4. 1.0% ethylol dodecyl biguanide acetate 19. 4 20. s 0. o 76. 1 23. 9 0. o

Diethylenc triamine 0.6% Tricthylcne tetramine. 07.5 2.5 0.0 94.0 6.0 0.0

Tetraethylene pentamlne. 0.4% ethylene dlamine 99. 9 0. 1 0. 0 99. 2 0. 8 0. 0 0.3% ethylene diamine 85. 9 14.1 0. 0 0.3% ethylene diamine 87. 4 12. 4 0.2 93. 5 6.5 0. 0 0.32% ethylene diamine 88. 6 11.2 0.2 90. l 9. B 0.0

260. CHHVHSTRY, catscommunes.

These examples indicate that the percentage of crystals less than 2.5 microns wide by actual count was increased from 30.7 fo the unmodified or "Blank" example to 79.4 or more by the use of ethylol dodecyl biguanide acetate. The mixed amines were almost as effective but required about twice as much modifier.

In the following examples each run consisted of a charge of 20.5 pounds of crude nitroguanidine and 275 pounds of water mixed in an autoclave at 100 C. The solution was then transferred to a blowcase and sprayed through inch jet into an enclosed spray chamber containing a circulating charge of 300 pounds of water. In order to accelerate the cooling of the batches to 25 0., air was drawn through the chamber at the rate of 600 cu. ft. per minute. The temperature of the blowcase was held at l02-105 C. and the spraying pressure was maintained at 100 pounds per square inch. In each run, the crystal size was varied by the use of ethylene diamine of the strength indicated. This was added to the charge and to the bath. The pH of the charge was adjusted with acetic acid after the addition of the ethylene diamine. The precipitated nitroguanidine was separated from the residue by centrifugal action or by filtration and the crystalline product was subsequently washed with water alone or. preferably, with water containing 0.1 per cent of ethylol dodecyl biguanide acetate.

The residual mother liquor from each run was used to make up the next charge and batch, sufficient water and ethylene diamine being added to compensate for that lost in the ecrystallization and by evaporation.

EXAMPLE 10 Batch 1 [\Vidth of crystals 4 microns] Weight of ethylene di amine used Per cent eth ylene diamine Weight of nitroguanidine Run No. D

Lbs.

EXAMPLE 1 1 Batch 2 [Width of crystals 3 microns] Weight of ethylene diaminc used Per cent ethylene diamine Weight of nitroguan id ine Run No. D

By actual microscopical count the percentage of crystals varying in width from 1 micron to 5 microns was as follows:

Ill)

ElAiv'iiiiER EXAMPLE 12 Batch 3 [Width of crystals 5 microns] Weight of Per cent Weight of Itun No. ethylene ethylene pH nitroguanidiamiue used diamine dine Gr. Lbs.

253 0. 4 7. 0 i7 286 U. 4 7. 0 i5 525 0. 4 8. 0) 329 U. 4 8. 0) l5 Total i09 In addition to the preparation of nitroguanidine in the form of very finely divided discrete crystals by the process of this invention, various other substances can be prepared in a similarly minute crystalline condition. Thus mercury fulrninate, lead azide, nitro amino guanidine and its salts, as well as picric acid, tetranitraniline and the like, can be prepared and a definite control of their minute crystalline shape, size and form can be efiected with the aid of the various modifier oi crystal habit herein described.

Various methods can be used to effect the desired crystallization. For example, spray cooling chambers may be utilized or spraying the solution in the form of fine streams into, or preferably under, an ice-water bath are among various other methods which can be used for the sudden cooling or chilling of solutions in order to precipitate the solute in finely divided form.

The very fine crystalline materials thus prepared find use in the manufacture of explosives. For example, a more highly effective type of explosive, namely a more powerful cordite, is obtained when such very fine crystals of nitroguanidine are used as can be prepared in accordance with the principles of this invention.

In particular, the use of such small crystals of nitroguanidine as above prepared in plastic cordite results in a greatly accelerated rate of propagation of the flame upon explosion and, moreover, it has been found that the oxidation of cordite is directly dependent upon the degree of subdivision of the crystalline nitroguanidine used. Thus, it has been definitely established that the small crystals of nitrcguanidine produced in accordance with this invention are far more desirable for incorporation in cordite than the larger crystals heretofore used.

In addition to such modifying agents as the amino and similar nitrogen containing compounds given above, various others may be used. Among such compounds the following may be more specifically cited. These are classified as markedly effective, efiective and slightly effective in the modification of crystalline habit.

A. Markedly effective:

Ethylol dodecyl biguanide acetate Ethylol dodecyl biguanide hydrochloride Casein (dissolved in dilute NHOH) Casein (dissolved in dilute sodium tetraphosphate solution) Corn oil condensed with monoethylol cyanamide Ethylene diamine Ethylene diamine+acetic acid Ethylene diamine-l-HzSO4 Ethylene diamine-l-HCI Glue Mixed diethylene triamine, triethylene tetramine, and tetraethylene pentamine+acetlc acid Mixed diethylene triamine, triethylene tetramine, and tetraethylene pentamine Phenyl biguanide Soy bean fatty acids condensed with monoethylol cyanamide Soy bean protein (dissolved in dilute sodium tetraphosphate solution) Tetraethylene pentamine+acetic acid B. Effective:

(Di-ortho-tolyl guanidine) 2ZI1C12 (Diaryl dithiophosphoric acids) +thiocarbanilide Ethylol dodecyl guanidine acetate Hexa or octadecyl guanidine acetate Sodium salt of diisopropyl dioctyl sulfosuccinic acid+pine oil Al2(SO4) z(diphenyl guanidine) s Castor oil fatty acids condensed with monoethylol cyanamides Cominaol (contains nitrogen) Cyanaceto guanamine u-2-cymel biguanide hydrochloride Cyanurea Ethylidene m-o-tolyl biguanide hydrochloride Furfural (mixed) xylol biguanide Gelatin Glutamic acid Glycine Guanidine thiocyanate p-Methoxy butyro guanamine Methylene o-tolyl biguanide Monoethylol cyanarnide condensed with ethylene diamine Phenyl biguanide carbonate Pyridine: HBr

a-Tertiary amyl phenyl biguanide hydrochloride a-Mixed xylyl biguanide hydrochloride C. Slightly effective:

Acetamidine anthranilate p-Amino acetophenon Benzylidene u-tolyl biguanide hydrochloride Benzoguanamine-2-sulfonic acid Black Liquor Soap condensed with monoethylol cyanamide Sec. butyl phenyl biguanide hydrochloride o-Carbamyl benzoguanamine Coconut oil-Polyethylene amines condensed with same Corn sugar Dextrin Diethanol amine Dimethylol urea Ethylidene a-(sec. butyl phenyl) biguanide hydrochloride Ethylidene a-(o-tolyl) biguanide hydrochloride p-Ethoxy butyro guanamine Guanidine carbonated-acetic acid Guanldine carbonate Gum arabic 1.3 diethylol 5-butyl biguanide diacetate Glutaro guanamine Di-ortho-tolyl guanidine Hydrochloric acid Di-phenyl guanidine Hexamethylene tetramine Di-xylyl guanidine Hydroxyl amine hydrochloride (Di-ortho-tolyl guanidinehSnCh 5 Meta-nitro aniline Morpholine biguanide sulfate Nitric acid Pentaerythritol Phosphoric acid Pierolonic acid Piperazine hexahydrate Resorcinol Acid salts of the condensate of a fatty acid and ethylene diamine Water soluble glucosides-i-methyl cellulose-{- a wetting agent Sebaoo guanamine Theanthrol, sodium lignin sulfonate a-p-Di-o-tolyl biguanide Thus, the general effect of such modification of crystal habit cannot be definitely attributed to any specific group and/or groups of elements, nor is it limited to either organic or inorganic compounds.

No completely satisfactory theoretical explanation of the manner in which these modifying agents function, other than that above given, can be ofiered. Moreover the modifying agents themselves do not fall within any recognized class, or appear to have any property in common other than their ability to change the crystal habit of nitroguanidines and substances similar therewith so as to yield extraordinarily small crystals.

It is to be understood that the examples, although drawn to the preparation of finely crystalline nitroguanidine are not to be deemed limited thereto. The invention in its broader aspects embraces the treatment, by the above described process, of various other organic compounds which are relatively soluble at higher temperatures such as those of boiling water and other boiling solvents and which when cooled form supersaturated solutions which readily precipitate out the solute in crystalline form. For these reasons the descriptive examples are to be taken as specific illustrations of the principles of the invention which is to be limited solely by the scope of the appended claims.

We claim:

1. The method of preparing finely divided nitroguanidine which comprises forming an aqueous solution of nitroguanidine at a temperature above C. but below the decomposition temperature of nitroguanidine, adding from 0.3 to 3% of ethylol dodecyl biguanide acetate and cooling the solution to precipitate the nitroguanidine in a finely divided form.

2. The method of preparing finely divided nitroguanidine which comprises forming a saturated solution of nitroguanidine in boiling water, adding from 0.3 to 3% of ethylol dodecyl biguanide acetate and cooling the solution to precipitate the nitroguanidine in a finely divided form.

3. The method of preparing crystalline nitr0 guanidine of the order of at most 2.5 to 5 microns in width and 20 to microns in length which comprises preparing a hot aqueous solution of nitroguanidine, adding from 1 to 3% of ethylol dodecyl biguanide acetate and cooling the solution to precipitate the nitroguanidine in a finely divided form.

GEORGE H. FOSTER EMIL F. WILLIAMS 

